They have bottle dates on everything they put into bottles. You need to do a little bit of (extraordinarily basic) math to decode it, but it's all there. It's in black ink, usually on the shoulder or neck of the bottle, and the first three digits indicate the day of the year that it was bottled (i.e., "042 . . ." = 42nd day of the year, so February 11). I added an ellipsis because there's a few other numbers afterwards, the meaning of which I'm not sure how to decode but I'm almost positive it refers to batch information.